1. Field of the Invention:
This invention relates to a motor and more particularly to a motor of the kind receiving power supply to its exciting coils under change-over control which is performed by detecting, with a position detecting element such as a Hall element or the like, the magnetic pole position of a rotor consisting of a permanent magnet. The invention further relates to the shape of the motor which is oblongly formed as a whole by arranging a pair of yokes which carry the exciting coils, with the rotating shaft of the rotor centered in between them, to be opposed to each other across the rotation shaft either in a line or in an angle somewhat narrower then 180 degrees.
2. Description of the Related Art:
The applications of the motors of the kind related to this invention include the drive source of an imaging apparatus such as a camera. Description of the prior art related to the motor of an imaging apparatus which is disposed within a lens barrel and arranged to shift an optical member such as a lens is as follows: Within the lens barrel, the blades of a stop device, a focusing lens, a zooming lens, etc. are arranged to be moved by the driving force of the motor. The known literature pertaining to stop blade and lens driving devices includes, among others, the following:
U.S. Pat. Nos. 3,687,042; 4,113,359, 4,152,060, 4,534,624 and 4,456,356.
The motors disclosed by these patents of the U.S.A. can be divided into two types including one type in which a pencil shaped cylindrical motor is disposed in a void space within a lens barrel and the other in which a hollow, cylindrical motor is disposed within a lens barrel. The pencil type motor which is disclosed, for example, in U.S. Pat. No. 4,456,356 necessitates some contrivance to reshape the lens barrel for obtaining the void space in which the motor can be disposed and for elimination of protrudent parts in the space. Meanwhile, the hollow cylindrical motor which is arranged, for example, as disclosed in U.S. Pat. No. 4,534,624 excessively increases the size and weight of the lens barrel.
The conventional motor used as above stated has been arranged in varied kinds according to the parts to be driven within the imaging apparatus, such as the camera body and the lens barrel of a camera using a silver-halide film, a floppy disc of an electronic camera (or still video) using a magnetic film.